The electrical characteristics of certain semiconductor devices such as Schottky barrier diodes are significantly degraded as a function of pressure applied to the junction area. Such devices therefore require extensive multi-piece packaging schemes to avoid damage to the chip or degradation of the electrical characteristics thereof. Such a packaging method is shown, for example, in U.S. Pat. No. 3,178,796.
The DO-35 package is a reliable, hermetic, glass-to-metal seal, semiconductor package consisting of two identical stud-leads 10 (hereinafter referred to as studs and typically of Dument or other suitable lead material) and a glass sleeve 12 as shown in FIG. 1. While its assembly is simple, fast and efficient, the package does rely on pressure contact of the studs directly to the semiconductor chip for electrical connection of, for example, the anode and cathode of a diode to the package leads. After assembly, the entire assembled unit including chip 11 is heated to a temperature of approximately 700.degree.C to obtain the hermetic glass-to-metal seal. As the package cools, additional pressure is applied to the chip as a result of the contraction of the glass as it cools to room temperature. Schottky barrier diodes of conventional design (contact button on top of the junction area) show degraded characteristics after this sealing process.
The effects of high temperature on the metallization and chemical integrity of the diode chip must also be considered. For a Schottky barrier diode, the metallization must achieve the desired barrier height and exhibit good adhesion to Si, SiO.sub.2 and Si.sub.3 N.sub.4. In addition, undesirable chemical reactions between package impurities and the diode chip during the sealing process must be prevented.
There are several chip configurations which overcome the difficulties discussed above. One configuration incorporates a relatively thick glass layer which covers the entire chip surface except that area immediately surrounding the junction. The metallization is then deposited over the diode junction area and extends over the top of the glass layer. The additional pressure developed by the package glass sleeve as it contracts during cooling from the sealing temperature is thus transferred via anode stud and glass layer to the chip area remote from the sensitive junction area.
In another configuration, the metallization scheme includes several contact pads remote from the junction area which the anode stud contacts. Thin metal fingers provide electrical connection between the metallization covering the diode and the contact pads. Again, the increased contact pressure received from the studs as the glass package contracts is transferred to the chip via the contact pads at some distance remote from the diode junction.